Five things to watch for in Tuesday's primaries

(CBS News) The nomination fight continues Tuesday as voters in Wisconsin, Maryland and Washington, D.C. head to the polls. Here are five things to notice.

Wisconsin is crucial ... for Santorum

It would be embarrassing for Mitt Romney if the front-runner fails to pull out a win in Wisconsin after Rep. Paul Ryan, the popular lawmaker who has become the Republican heavyweight on the budget, endorsed him and campaigned with him for the past several days. Furthermore, Romney and the super PAC supporting him, Restore our Future, continued their advertising advantage in Wisconsin. According to Restore our Future, the organization has spent $2.3 million in Wisconsin compared to $660,000 reported by the Red White and Blue Fund, a super PAC that supports Rick Santorum.

Romney is the heavy favorite, but it is Rick Santorum who needs to win the state. If Romney wins Wisconsin, it's another thumb press on the scale that may make it impossible for Santorum to overcome Romney in the race for 1,144 of 2,286 delegates to clinch the nomination.

And a Santorum upset would give him momentum for the upcoming primaries, where his chances are better, including in his home state of Pennsylvania. Santorum also needs the delegate boost as Mitt Romney leads him by more than 300 delegates, according to CBS News projections. (Romney has 554 delegates compared to Santorum's 241 delegates.)

Further, the former Pennsylvania senator needs to win because he worked hard there. According to the Milwaukee Journal Sentinel, he campaigned in 22 counties compared to Romney, who visited five and focused on the vote-rich ones.

But it's going to be a tough race for the former senator. An NBC/Marist poll released last week gave Romney a seven-point lead over Rick Santorum, and that poll was released before Romney's high-profile endorsements.

DC and Maryland vote, too

All eyes have been on Wisconsin as the next big state, but voters in Maryland and Washington, D.C. head to the polls, too. Considered to be easy wins for Romney, both contests could help him collect delegates.

Rick Santorum is not even on the ballot in D.C, where 16 delegates are at stake in the winner-take-all primary.

In Maryland, despite being Pennsylvania's southern neighbor, Santorum has not spent any time campaigning there as conservative and religious voters attracted to the former Pennsylvania senator are relatively rare in Maryland. According to exit polls from the 2008 Republican primary, only one in four voters identified as "very conservative" while 39 percent said they are "moderate/liberal."

With 53 delegates at stake between the two contests, Romney would be more than halfway to collecting the necessary delegates.

Who votes for Romney?

According to exit polls in the 2008 Republican primary, 34 percent of voters identified as "white evangelical" and 27 percent as "very conservative," voters that Rick Santorum have been winning over handily in previous states.

Who will they support in Wisconsin?

If Santorum fails to win, or loses support among these demographics, it could mean that Santorum is losing support or that Republicans are anxious to wrap up the primary. Or both.

Voter turnout

After Wisconsin, Maryland and D.C. vote tomorrow, voters in 35 contests will have had their say in this marathon Republican primary. Are voters fatigued? Long primaries mean that states that vote later in the process matter, which could spur higher turnout. But fatigue is often a risk when the primary fight wages on, especially as the campaigns run negative advertisements, which has been the case this campaign.

Wisconsin is an open primary, which means any registered voter can participate. It will also be interesting to see how many people identified as Democratic or liberal turn up to the poles. Their vote could be a strategic vote to keep the Republican primary going or a voter disillusioned with President Obama.

The future for Newt Gingrich and Ron Paul

Former House speaker Newt Gingrich and Texas Rep. Ron Paul are still in the race but both have sharply cut back their campaign schedules. On CBS News' "Face the Nation" Sunday, both candidates pledged to stay in the race until the convention in August, with Gingrich hoping for a brokered convention where no candidate is achieved the nomination. Paul has tacitly acknowledged that his goals are to change the conversation and "save the Republican Party from themsleves."